JPS61112394A - Embedded type semiconductor laser - Google Patents

Abstract

PURPOSE:To maintain a single lateral mode even if high output power is implemented, by providing double light guides, in which another light guide mechanism is provided in one light guide, thereby broadening the width of an active layer, which is determined by the width of a mesa part, and enlarging the cross sectional area of the light guides. CONSTITUTION:A mesa part 100 is provided on a semiconductor substrate 1. In the structure of the mesa part 100, a first semiconductor layer 30 of P type Al0.3Ga0.7As, whose forbidden band width is larger than an active layer 4, is held by a second semiconductor layer 20 of N type GaAs, whose forbidden band width is smaller or equal to the active layer 4. The active layer 4 is positioned so that the upper part and the lower part of the mesa 100 are separat ed. Therefore, the active layer 4 at the side of the upper part of the mesa is surrounded by a clad layer 5 of N type Al0.3Ga0.7As, whose refractive index is smaller than that of the active layer. Thus one light guide is formed. Light is guided in the light guide having a width W1. Even if the width W1 is made broad, a single lateral mode is maintained owing to the presence of an inner light guide having a width W2.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a buried semiconductor laser that oscillates in a stable single-transverse mode and provides high output.

(Prior art and its problems) Semiconductor lasers are used as light sources for optical communication and optical information processing, but in these applications, semiconductor lasers must oscillate in a stable single-transverse mode and have high output. is important.

Currently, as semiconductor lasers for these light sources, a structure called a buried structure (hereinafter abbreviated as BH tank structure) in which an active layer is embedded in a semiconductor layer whose refractive index is smaller than that of the active layer is often employed. However, when the width of the active layer embedded in a buried semiconductor laser becomes 2 μm or more, higher-order transverse modes easily oscillate, and at low implantation levels, even single-transverse mode oscillations result in high output operation. Therefore, there is a problem that if a large amount of carriers is injected, single-transverse mode oscillation cannot be maintained.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned problems and provide a buried semiconductor laser which oscillates in a stable single-transverse mode and provides high output.

(Means for Solving the Problems) In the buried semiconductor laser of the present invention, a first semiconductor layer having a larger forbidden band width than the active layer is formed on the substrate, and a second semiconductor layer having the same or smaller forbidden band width than the active layer is formed on the substrate. The present invention is characterized in that a mesa having a structure sandwiched between semiconductor layers is provided, and a double heterostructure having an active layer separated at the upper part of the mesa and the lower part of the mesa is provided on the substrate including the mesa. Therefore, since the active layer above the mesa is embedded in a semiconductor crystal having a smaller refractive index than the active layer, it forms one optical waveguide. Furthermore, inside the active layer that forms the four optical wave paths at the top of the mesa, the forbidden band width of the semiconductor forming the mesa is larger at the center of the mesa and smaller on both sides of the mesa than the forbidden band width of the active layer. Therefore, it has a double waveguide with another waveguide mechanism inside the optical waveguide. This makes it possible to maintain a single-transverse mode even when the active layer width determined by the mesa width is widened to increase the cross-sectional area of the optical waveguide to achieve high output.

(Example) This will be explained in detail below using the drawings.

FIG. 1 is a sectional view of an embodiment of the buried semiconductor laser of the present invention, and the isometric refractive index distribution of the waveguide mechanism is also shown in the upper part.

A mesa 100 is provided on a semiconductor substrate (P-type GaAs) 1, and the mesa 100 is made of a first semiconductor layer (P-type Ate, 3 Ga) having a larger forbidden band width than the active layer (GaAs) 4.
0.7As) 30 is a second semiconductor layer (n-type GaAs) 20 whose forbidden band width is smaller or equal to that of the active layer 4.
It has a structure in which it is sandwiched between two. The active layer 4 is located separating the upper part of the mesa 100 into the lower part, and therefore the active layer 4 at the upper part of the mesa is surrounded by a rad layer 5 having a smaller refractive index than the active layer 4, and forms one waveguide. is formed. The waveguide width is WI as shown in FIG.
It is. The active layer 4 on the mesa 100 is a thin cladding layer (P
The portion A is in contact with the first semiconductor layer 30 and the portion B is in contact with the second semiconductor layer 20 via the type AtO, 3Ga0.7As) 3. The first semiconductor layer 30 has a larger forbidden band width than the active layer 4, and the second semiconductor layer 20 has a larger forbidden band width than the active layer 4.
.

The forbidden band width is smaller or equal. Because of this, a waveguide structure with a width W2 is further provided inside the active layer 4 on the mesa. If the waveguide of the active layer 4 is replaced with an equilateral refractive index waveguide, the shape shown in the upper part of FIG. 1 will be obtained.

The light is guided by a waveguide with a width of Wl, and the internal W
Due to the existence of a waveguide with a width of 2, even if the width of W is increased,
Landscape mode is maintained. The ability to widen the width of Wl means that a large output can be produced, and even at that time, the unilateral mode is maintained.

Hereinafter, a method for manufacturing a buried semiconductor laser according to the present invention will be explained. Figure 2 fa), (bl, (C),
(d) is a diagram showing the manufacturing process of the semiconductor laser of the present invention. As shown in FIG.
P-type At013Ga with a thickness of 1 μm becomes the semiconductor layer 30 of
0.7As, fil was prepared using an organometallic decomposition method (hereinafter referred to as MOCVD).
As shown in Figure (b) K, Si
After forming the stripe mask 200 of MOCV
Vapor phase etching is performed inside the D furnace reaction tube, and then an n-type GaAs layer that will become the second semiconductor layer 20 is grown to form the shape shown in Figure (C). Next, 5in2200 was removed, and after etching, a P-type At0.3Ga0.7As layer, which would become the first cladding layer 3, was grown by liquid phase epitaxial growth to a thickness of 0.2 μm.
s layer 0.1 μm 1 n-type At which becomes the second layer 5
An O,3Ga0.7As layer was grown to a thickness of 2 μm to fabricate the semiconductor laser structure of the present invention shown in FIG. 3(d). In reality, a GaAs carapace layer is further grown on top of this, but it is not shown in the figure. Although the upper active layer 4 and the lower active layer 4 of the mesa 100 are separated, such separation growth can be easily performed by liquid phase epitaxial growth.

(Effects of the Invention) As described above, in the present invention, since the active layer has a double waveguide structure, high output and single-transverse mode oscillation can be easily obtained.

In addition, since the second semiconductor layer has a conductivity different from that of the semiconductor substrate, a P-n-P-n structure is formed in areas other than the central part of the mesa, and therefore, a P-n-P-n structure is formed only in the light emitting region of the active layer and most in the lateral fundamental mode. The implantation is performed with a width of W2 shown in FIG. 1, which provides a large gain. This, in combination with the waveguide mechanism, is also convenient for single-transverse mode oscillation.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the embedded semiconductor laser of the present invention, and FIGS. 2(a), (b), (C),
(d) is a manufacturing process diagram of the semiconductor laser of the present invention. In the figure, 1... semiconductor substrate, 3, 5...
Cladding layer, 4...Active layer, 20...
Second semiconductor layer, 30...First semiconductor layer, 2
00...5in2 stripe.

Claims (1)

[Claims] A mesa having a structure in which a first semiconductor layer having a forbidden band width larger than that of an active layer is sandwiched from the sides by a second semiconductor layer having a forbidden band width equal to or smaller than that of the active layer is provided on a semiconductor substrate. 1. A buried semiconductor laser characterized in that a double heterostructure having an active layer separated at an upper part of a mesa and a lower part of the mesa is provided on a substrate including the mesa.